The present invention generally relates to devices and methods for occluding septal defects or shunts in the heart or the vascular system. In particular, the present invention provides a device for closing such defects which may be delivered through a catheter and a method for delivering and deploying that device to close off the defect.
A septum is generally defined as a thin wall of muscle or other tissue which divides two or more chambers or other areas within the body. The term "septal defect" generally refers to a perforation or other hole which passes through a septum. Ventricular septal defects, atrial septal defects and patent ductus arteriosus are the three most common congenital cardiac malformations. Of these three malformations, atrial septal defects are the easiest to approach through a transcatheter approach and the defects themselves are located away from the atrioventricular valve apparatus. These defects have been surgically corrected for decades.
Initially, atrial septal defects were corrected by open heart surgery. In such an operation, the surgeon would have to open the chest of a patient and bypass the heart temporarily, e.g., by means of a mechanical heart or a "heart-lung machine." The surgeon would then physically cut into the heart and suture small defects closed. In the case of larger defects, a patch of a biologically compatible material would be sewn onto the septum to cover the defect. An atrial septal defect makes the heart muscles work considerably harder because of shunting of blood through the defect and, if left untreated, leads to high pulmonary arterial pressures, and this additional strain placed on the heart muscles can cause fatal heart failure.
In order to avoid the morbidity and mortality associated with open heart surgery, a variety of transcatheter closure techniques have been attempted. In such techniques, an occluding device is delivered through a catheter. Once the closure device is positioned adjacent the defect, it must be attached to the rest of the septum in a manner which permits it to effectively block the passage of blood through the defect.
The first such closure device was proposed by King and Mills nearly 20 years ago and is described in U.S. Pat. No. 3,874,388 (1975), the teachings of which are incorporated herein by reference. The King closure device comprises a pair of complex mechanical umbrellas, with each umbrella having a plurality of arms extending radially from a central hub. The hubs of the two umbrellas are mechanically connected to one another and each umbrella includes a fabric covering over the arms, much like a common umbrella. The ends of each arm are provided with barbs which are anchored into the septum to hold the occluder in place. Although this device represents a significant improvement over open heart surgery, the complex mechanical umbrellas prove rather difficult to unfold after passage through a catheter, requiring an array of cables to deploy the arms. This makes proper placement of the device difficult, and the barbs on the arms prevent retraction or repositioning of the device once it is in place. Use of this device has been limited to adult patients because the device requires a large catheter, such as about 23 French (7.3 mm), for delivery.
Rashkind proposed a single-umbrella closure device which was capable of delivery through a 5 mm system, which permitted use in children weighing at least about 20 kg. Similar to the King device, this umbrella utilizes barbed hooks on the ends of umbrella arms to ensure attachment to the septum, and the single umbrella is placed on the left side of the atrial septal defect. The barbs once again prevented disengagement of the device, and poorly centered devices were common. This device had limited acceptance in the field due to the positioning difficulties because malpositioned or improperly seated devices frequently required open heart surgery for correction.
Due to the low success rate of these devices, Lock and others developed a "modified double-umbrella Rashkind occluder" in which the arms of the device are hinged to permit them to fold back against themselves. Lock's "clamshell" occluder did not include barbs at the end of the radial arms of the umbrella, allowing its position to be readjusted or retrieved. Furthermore, the structure of this umbrella was somewhat more compact than the earlier King or Rashkind umbrellas, allowing delivery through an 11 French (3.7 mm) catheter, enabling the device to be used to treat children weighing 8 kg or more.
More recently, Sideris has proposed an occlusion device which combines a single umbrella with a separate anchoring device. This occluder is shown in U.S. Pat. No. 4,917,089. Like the previous defect occlusion devices, Sideris' invention utilizes an umbrella with a plurality of radially extending arms. A string connects the arms of this umbrella to a generally rhomboidally shaped anchor which includes an internal wire skeleton and a central, rhomboidally shaped piece of rubber. The string attached to the struts of the umbrella is affixed to the central rubber element of the anchor. The anchor is placed on the opposite side of the septum from the umbrella and the length of the string limits movement of the occlusion device with respect to the septum.
All of the prior art devices described above share two defects in common. Firstly, all of these systems are rather mechanically complex and require a great deal of remote manipulation for deployment, such as by applying tension to one or more cables in order to deploy the arms of an umbrella or to anchor the device in place. This extensive remote manipulation not only increases the difficulty of the procedure, but tends to increase the likelihood that the device will be improperly deployed and require either retrieval or repositioning.
Secondly, all of these devices are essentially two separate members which are joined to each other at a single point or pivot. When the left atrial member is opened, the central point would tend to ride to the lower margin of the defect; proper centering of the device is quite difficult. The Lock device does form a `cone` when traction is applied to help centering. In order for this to effectively occur, though, the device has to be pulled perpendicular to the plane of the atrial septum. In a beating human heart, this is rather difficult to achieve.
It would therefore be desirable to provide a simple, compact closure device which may be delivered through a small catheter to permit the treatment of younger children. It would also be highly advantageous to have such an anchoring device which can be readily deployed with a minimum of remote manipulation. In addition, a device which is truly self centering and self occluding would be superior to these prior art devices.